The present invention relates to packet switching systems and network configurations, and in particular to an apparatus and a network configuration suitable for signal processing in a synchronous transfer mode (ATM) switching networks for switching fixed length packets.
Currently, in ITU-T (International Telecommunication Unionxe2x80x94Telecommunication standardization sector), standardization works of various recommendations for implementing the Broadband ISDN are under way. The Broadband ISDN aims at providing service with a line rate of 156 Mbits/sec, for example, to users by adopting an ATM switching method.
As for a method for implementing signal processing in switching systems implementing the ATM switching method (hereafter referred to as ATM switching systems), a method described in U.S. Pat. No. 5,214,642 is known. According to this method, signal processing is implemented by connecting subscriber lines and trunks to a signal processor via an ATM switch. Since the signal processor is shared by a plurality of subscriber lines and trunks via the ATM switch, an economical ATM switching system is implemented.
As for the ATM switching system for implementing the Broadband ISDN, signals of a large number of users undergo high speed processing and consequently a system of high reliability is needed. As a measure for maintaining communication in the event of a failure of a part of the ATM switching system, therefore, reliability improvement such as a conventionally known redundant configuration in the switching system is attempted as represented by xe2x80x9cduplication,xe2x80x9d for example. In the xe2x80x9cduplicatedxe2x80x9d configuration, functional blocks forming the ATM switching system, such as the switch, signal processor and processor, are duplicated block by block. In the case where one of the duplicated blocks fails, switchover to the other is conducted. Even when a fault has occurred, therefore, the normal state is quickly restored.
Furthermore, in the conventional ATM switching system, a signal processor is installed for each ATM switching system and a function of setting/releasing an information channel in response to a request from a user is implemented. The SVC (Signalling Virtual Channel) function is thus implemented.
In the conventional known ATM switching network, contrivances have been effected. For example, the signal processor is shared in the ATM switching system. Configuring the ATM switching network with due regard to securement of reliability and provision of a wide variety of communication services causes complicated configurations of switching systems and the whole network because of adoption of redundant configurations, resulting in an increased cost. As for the process of spread of the Broadband ISDN, large-scale switching networks forming a trunk line network having a large capacity are introduced at the beginning in the same way as the process of construction of the conventional networks. In this case, however, the number of subscribers subject to signal processing is very large. Even if there is a cost increase as described above, therefore, the cost increase per subscriber is suppressed to a relatively small value and consequently no problems are posed. When introduction of the Broadband ISDN has finally advanced to introduction thereof to small-sized communication facilities and communication networks, such as LANs and private switching networks, accommodating a small number of subscribers, a cost increase per subscriber becomes very large provided that a system configuration similar to that of a large scale switching network forming a trunk network as described above is used. Because communication services and traffic conditions applied to these small scale switching networks are different and diverse, and a smaller number of subscribers are accommodated by these small scale switching networks.
Owing to the progress of hardware techniques, there is presently little probability that hardware such as switches gets out of order. On the other hand, the number of steps of software for executing call control and the like has become large in order to implement various functions attendant upon introduction of intelligent networks (INs) for providing various communication services. The proportion of faults caused by software is thus increasing. In such a situation, duplication of each device in the switching network is not effective in many cases for relief in a fault caused by software and improvement of reliability and it increases the device complexity. For forming and spreading broadband communication systems and communication networks hereafter, it is important to take a reliability improving measure narrowed down to software faults.
Furthermore, in order to cope with the increase of IN functions, the processor executing the call control and the like is needed to have a greater processing capability year after year. In the present configuration of switching systems and switching networks, however, it is not easy to replace the processor of a switching system with that having a higher performance and a cost for replacement is also needed.
In view of the situations heretofore described, the present invention has been made.
An object of the present invention is to provide a switching system and a configuration and processing procedures of a switching system capable of easily continuing the signal processing in the event of occurrence of an abnormality such as a fault or an overload state in a call control processor in the switching system.
Another object of the present invention is to provide a switching system and a configuration and processing procedures of a switching system capable of easily enhancing the processing capability even when the processing capability of the call control processor in the switching system or the signal processor executing processing of the layer 2 or below of a signal channel has become insufficient.
Another object of the present invention is to provide means for implementing an ATM switching network, capable of easily providing the SVC function.
Still another object of the present invention is to provide, even for a small scale network such as a LAN or a private network, an ATM switching system and an ATM switching network having signal processing procedures and means capable of solving the above described problems and having an economical configuration.
In accordance with the present invention, upon occurrence of an abnormality such as a fault or an overload state in a call control processor included in an ATM switching system, another switching system in the network is informed of this fact and signal processing is continued by using a call control processor of the switching system thus informed.
In the conventional technique, a line interface and a controller (which is a processor in many cases) installed outside the line interface are connected together via a control line and contents of a header transformation table included in the line interface are rewritten via the control line. In the present invention, however, contents of a header conversion table included in a line interface are rewritten by using a control cell produced in a controller such as a processor installed outside the line interface and an input cell is outputted to a desired output port of an ATM switching system according to the communication situation.
In the present invention, the line interface and the controller are not connected together via a control line and a control cell can be sent to the line interface in the same way as an ordinary cell. In the case where a processor of an ATM switching system A which operated normally until then has ceased to operate due to a failure or has been overloaded, for example, therefore, the operation of the ATM switching system can be controlled by a processor of another ATM switching system B.
In accordance with the present invention, when three or more ATM switching systems are connected to form an ATM switching network, at least one specific switching system is used as a switching system dedicated exclusively to backup.
In accordance with the present invention, when three or more ATM switching systems are connected to form an ATM switching network and a fault has occurred in a certain ATM switching system, an adjacent ATM switching system is used as a backup switching system every route of each signal connection which has been administered by the faulty switching system.
In accordance with the present invention, an ATM switch is connected to a signal processor via a line interface device.
In accordance with the present invention, control of path in a ATM switch for a cell inputted to a plurality of ATM switching systems having no signal processors (hereafter referred to as ATM-HUB), i.e., header conversion table rewriting is executed by a certain specific ATM switching system connected in a switching network or a certain specific external call controller. Hereafter, an ATM switching system for an office is referred to as ATM-PBX.
In this case, a cell is produced by a signal processor of a specific ATM switching system installed outside the ATM-HUB or of an external call controller and sent to a line interface included in the ATM-HUB. Contents of the header conversion table are rewritten by using this control cell to control the transfer of inputted cells in the ATM-HUB.
In the present invention, when an abnormality such as a fault or an overload state has occurred in a call control processor included in the ATM switching system, another switching system in the network is informed of this fact and this switching system effects call control as a substitute. Thereby, reliability of the ATM switching system can be improved without incurring a cost increase of the switching system due to duplication.
In the case where three or more ATM switching systems are connected to form an ATM switching network, only at least one specific switching system is used as a switching system dedicated exclusively to backup. Thereby, reliability of the ATM switching system can be improved without incurring a cost increase of the switching system in the same way as the foregoing description.
When a fault has occurred in one certain ATM switching system in the case where three or more ATM switching systems are connected to form an ATM switching network, an adjacent ATM switching system is used as a backup switching system every route of each signal connection which has been administered by the faulty switching system. Thereby, the reliability of the ATM switching system can be easily improved.
Furthermore, an ATM switch is connected to a signal processor via a line interface device and then the above described backup processing is conducted. Thereby, more signal processors or more call controllers can be easily installed in the case where the signal processing capability has become insufficient.
Furthermore, control of path in an ATM switch for a cell inputted to a plurality of ATM-HUBs having no signal processors is executed by a certain specific ATM-PBX connected in a switching network or an external call controller. Thereby, the SVC function can be easily implemented.
As apparent from the foregoing description, when a fault has occurred in a call control processor of a certain ATM switching system included in an ATM switching network according to the present invention, another ATM switching system is informed of this fact and information required for continuation of signal processing is transferred to the substitute ATM switching system. Furthermore, cells of a signal channel received by the faulty ATM switching system are also transferred to the substitute ATM switching system. Signal processing of the faulty ATM switching system is thus backed up by the substitute ATM switching system. Thereby, backup of signal processing can be easily implemented. This results in an effect that degradation of switching processing capability of the ATM switching network and suspension of switching processing are prevented.
Furthermore, when a call control processor of a certain ATM switching system has fallen into an overload state, another ATM switching system is informed of this fact and cells of a new signal channel arriving at the ATM switching system in the overload state are transferred to the substitute ATM switching system. The substitute ATM switching system conducts processing of the new signal channel as a substitute for the overloaded ATM switching system. This results in another effect that the load of signal processing in the ATM switching system can be distributed.
Furthermore, as a result of a signal processor being connected to an ATM switch via a line interface device, there is also brought about another effect that more signal processors and call controllers can be installed more easily.
Furthermore, a plurality of ATM-HUBs having no signal processors, and an ATM-PBX or an external controller form an ATM switching network, and path control in ATM switch of the ATM-HUBs (i.e., setting the header conversion table in the LIF) is executed by the ATM-PBX or external call controller. This brings about an effect that an ATM switching network effecting the SVC function can be implemented easily and inexpensively.